In many automotive lamp units such as taillight assemblies, the reflex reflector section of the assembly may exceed the effective reflective area that is required by regulation. This excess reflective area is usually due to the overall surface area of the lens being designed to comply with styled contoured surfaces of the vehicle, or the like. In such an arrangement, the reflex reflector portion may combine a so-called effective area, which actually provides the regulatory standard of reflectivity, as well as a simulated area which, while giving the appearance of an effective section, is in fact a section of a lower standard of reflectivity.
Due to the body contours of vehicles, particularly in the automobile designs of recent times where low drag coefficients have dictated the use of more smoothly rounded or contoured surfaces, a reflex reflector section may well be located in a complex curve of a taillight assembly. Further, if a simulated reflex reflector area extends into the curved portion of the assembly, then the manner in which the simulated area is applied in the manufacture of the mold of the lens becomes a deciding factor in manufacturing costs versus quality of appearance.
There are several well known methods of providing a simulated reflective area of quality appearance. One such method is the use of spark erosion in the manufacture of the mold. Another is the use of direct machining of the mold surfaces to provide a diamond surface. Yet another method is the setting up of a mold using a plurality of reflex prisms with multiple axes, a process in which there is a substantial shoulder area between adjacent prisms in the curved section thereof. This latter method, together with the spark erosion and direct machining methods of surfaces are all expensive.